Spinal stabilization can be achieved by providing an interbody implant. Some of these implants are bone, PEEK, solid titanium or similar non-bone implant material and some are hollow implants that provide for inclusion of a bone graft or other suitable material to facilitate bony union of the vertebrae.
Interbody implants can be inserted into the disc space through an anterior, posterior or lateral approach. In some systems, the implants are inserted into a bore formed between adjacent vertebral bodies in the cortical endplates and can extend into the cancellous bone deep to the cortical endplates. Implant size is typically selected such that the implants force the vertebrae apart to cause tensing of the vertebral annulus and other soft tissue structures surrounding the joint space. Tensing the soft tissues surrounding the joint space results in the vertebrae exerting compressive forces on the implant to maintain the implant in place.
It has been found desirable to keep the surgical opening as small as practical while still having sufficient room to insert the implant device and the end of an elongated tool or insertion instrument.
Advantageously, if the implant size could be reduced further that would allow the surgical opening to be reduced; however, once implanted the device needs to be expandable to provide sufficient spacing of the vertebrae.
A whole class of expandable interbody implant devices have been developed for this purpose. Some prior art devices use hydraulic expansion or inflatable balloons. Some devices are stackable elements piled on themselves to raise their height. Some use rotatable screw jack designs. Some are wedges that have a fixed hinged end and an opposite expandable end. All of the rotatable expandable devices using screw threads require the device to be round cylinders or posts.
One of the problems of such devices is the amount of post insertion manipulation required to reach a fully expanded properly space height is tedious and time consuming. Secondly, additional set screws or locking elements are often required to keep the device at its proper size. Thirdly, the devices of a circular shape are not the best fit for the adjacent vertebrae being spaced. Fourth, most of the devices have the internal space occupied with mechanisms limiting the amount of bone growth material available for packing the implants.
The wedge type implants generally contact the bone on an angle and expandable wedges when expanded simply expand on an angle not parallel to the vertebrae surface. This places localized high loading between the vertebrae because the wedge surfaces are not parallel to the vertebrae.
These and other limitations in the prior art have been corrected and solved by the present invention as disclosed herein.